From a paper by Nathaniel A. White II, DVM, MS, Diplomate ACVS, Virginia Tech; a few excerpts:

"Colic is one of the most difficult diseases to study due to the large number of diseases which create signs of colic."

"A recent study in Texas found an increased risk of colic associated with weather changes as recalled by owners of horses with colic."

"In a study in Virginia, seven cases of colic occurred during a snowstorm over a three-day period. This was unusual as there were only 104 cases of colic in the horses being studied for a full year."

"Most likely the focal increase in colic episodes was not directly related to the weather, but rather due to management changes caused by the weather."

Read the full paper here: Epidemiology of Colic.